In the United States, at least 10% of couples suffer involuntarily infertility. In Britain, there are about 600,000 infertile couples (Winston, 1991) and in the United States two million women are potential candidates for in vitro fertilization (IVF). Because IVF has a low success rate of 10--15%, multiple attempts and increasing costs are incurred to bring a pregnancy to term. Therefore, only a tiny proportion of the North American and European population currently in need can take advantage assisted reproductive treatments. The situation for infertile people is much worse in less medically developed countries.
Poor function of spermatozoa accounts for one quarter of all human infertility: IVF is one of the only effective treatments (Winston and Handyside, 1993). IVF can be done by transfer of oocytes and sperm in a synthetic medium into the fallopian tube (gamete intrafallopian transfer (GIFT)) or newly fertilized zygotes (egg and sperm put into a synthetic medium and fertilization allowed to proceed) are transferred into the fallopian tube (zygote intrafallopian transfer (ZIFT).
Pregnancy resulted from only a small percentage (13%) of transfers of a single presumably fertilized egg back into the female, but rose to 25% when four or more eggs were simultaneously transferred (Winston and Handyside (1993)). One of the primary reasons for the low rates of pregnancy resulting from IVF is believed to be inadequate culture media in which the egg and sperm are kept.
In IVF, poor sperm function does not allow enough sperm to contact and penetrate the egg. Most previous strategies to overcome the difficulties of IVF have involved various manipulations of the oocyte. For example sperm have been injected directly into the egg with a high success rate (Fishel and Timson, 1992). The disadvantages include potential damage to the chromosome spindle and high genetic risks, because abnormal sperm may be injected. Furthermore this technique increases patient cost dramatically, because of the time and expertise necessary to perform this operation, which frequently must be repeated multiple times.
Only recently has attention turned to enhancement of sperm motility parameters. It has been shown that sperm motility parameters are important for both presenting the maximum number of male gametes to the egg as well as facilitating penetration through its zona pellucida (Bedford et al. 1982). Sperm motility parameters have a high correlation with fertilization rates in vitro (Mahadevan and Trounson, 1984).
The only compound currently used to enhance sperm motility in vitro or in vivo is pentoxifylline whose efficacy is currently questioned. Pentoxifylline (3-7 dimethyl-1-5-oxohexylxanthine) is added routinely to spermatozoa in human IVF programs. Its efficacy is hotly debated in the scientific literature, since one study reported that it was not useful in enhancing sperm function in cases with previous IVF failure (Tournaye et al. 1993). Furthermore, two recent studies have indicated that pentoxifylline causes spermatic mutagenesis as does direct application of caffeine to these gametes (Barkay et al. 1984 and Harrison et al. 1980). Another study showed that oral administration increased sperm count and motility, but suggested that the effect may not have been any greater than that produced by ingestion of drinks containing caffeine, also a methylxanthine.
Although pentoxifylline did not increase sperm motility parameters in normospermic men, it had significant increases in these parameters in oligospermic samples. Nevertheless, when this drug was added to sperm from donors with a history of previously failed fertilization, there was only a 5.1% increase in the oocyte fertilization rate from 17.6 in controls to 22.7% in pentoxifylline-treated groups (Yovich et al. 1988). Also, recent studies have shown that pentoxifylline can only enhance significantly the fertilization rate when used within a brief time (30 minutes) prior to exposure to the egg. An added difficulty is that after incubation with pentoxifylline the sperm must be washed free of pentoxifylline and re-added to the oocyte due to the potential harmful effect of this drug on the egg (see Yovich et al. 1988).
There are currently no drugs other than pentoxifylline which are approved by the FDA for sperm motility enhancement. Furthermore, there are only scattered reports in the literature that other compounds are being tested. These include plasminogen activator, an endogenous protease, correlated positively with sperm motility (Lison et al. 1993), but there is no data suggesting a cause and effect relationship between the two. Acrosin, another endogenous protease in sperm, has no significant effect on sperm motility (Koukoulis et al. 1989) even though lower levels of this enzyme appear to be correlated with some abnormal semen characteristics (De Jong et al. 1993). Components of the oocyte may affect the fertilization rate (Hoshi et al. 1993; Winston and Handyside 1993) once the sperm and egg are in close proximity, but there currently are no data showing that these components enhance sperm motility. Hyaluronate and strontium added to the media slightly prevented sperm motility degradation (Psalti et al. 1993).
Male skates and rays have an accessory sex gland that produces a fluid (AGF) of alkaline pH (8-9) (Smith 1929). Prior to the present disclosure, the functions of this gland and the alkaline gland fluid were unknown.
The increased use of in vitro fertilization techniques by couples unable to bear children show a strong need for the use of the compositions and methods of the present invention, which will enhance sperm motility parameters and, thus, lead to greater oocyte fertilization. Artificial insemination programs for livestock also need the benefit of enhanced sperm motility. Likewise, there is also a need for a natural contraceptive for use in human vaginal contraceptive jellies and on condoms, because the current synthetic chemicals have either limited effectiveness or unknown long-term health effects. The present invention meets these needs by providing purified alkaline gland fluid and specific proteins that stimulate or decrease sperm motility.